The present invention relates generally optical transceiver devices for use in uncontrolled environmental conditions. More particularly, the present invention relates to controlling the operating wavelength tolerances of a Coarse Wavelength Division Multiplexed (CWDM) transceiver in an uncontrolled environment that may have an environmental temperature range of between −40° C. to 85° C.
It is known in the prior art that there is a need to maintain a laser device such, as an optical transmitter, at a relatively stable and constant temperature in order to optimize its performance characteristics and to maintain the output of the transmitter within a desired operational wavelength range. In this regard, semiconductor lasers used in optical transmitters have traditionally been packaged with thermoelectric climate control devices that are controlled and dynamically switched between a cooling mode and a heating mode. Such thermoelectric climate control devices were critical in the prior art in order to maintain the semiconductor laser at a constant temperature. The drawback to this packaging arrangement was that the size and power consumption of the optical transmitter package was greatly increased.
In order to reduce the cost, size, and power dissipation of these optical transmitter packages, there have been efforts to improve the performance of the laser diodes themselves by increasing their operational temperature ranges while maintaining their wavelength tolerances, thereby allowing them to be used without thermoelectric coolers over a wider temperature range. As a result of these efforts, relatively good performance wide temperature range lasers are now available and are used in many uncontrolled environmental applications.
Even with the improvements in the laser diodes, however, there are still significant performance issues related to lasers that operate in cold environments thereby creating the need for heating. For example, in the operation of CWDM transceivers, the allowed standard for wavelength tuning is 13 nm. The problem is that an uncooled distributed feedback (DFB) laser typically used in CWDM transceivers has a wavelength variation of 12.5 nm over the operational temperature range of between about −40° C. to 85° C. This 12.5 nm variation in laser wavelength leaves only a very small tolerance for the wavelength selection of the DFB laser. Accordingly, there is less than a 0.5 nm window available for selection of the initial wavelength of the DFB laser, a window that simply cannot currently be achieved with consistent results.
Even if it were possible to achieve consistent results within the available 0.5 nm selection window, various physical phenomena that have deleterious effects on laser performance are amplified at the lower end of the stated operational temperature range. For example, the pattern dependent turn-on delay increases significantly at low temperatures causing additional timing jitter. In addition, mode partitioning in DFB lasers, which are designed to operate over a wide temperature range, increases at low temperatures possibly resulting in an excessive dispersion penalty for the entire system.
There is therefore a need for an optical transceiver that has a reduced package size and power consumption as compared to prior art temperature controlled optical transceivers. The is a further need for an optical transceiver that is capable of operating in uncontrolled environmental conditions while also being capable of meeting the required 13 nm tolerances set forth in the CDWM standards. Finally there is a need for an optical transceiver that exhibits an improved performance by limiting the environmental temperature range under which the laser must operate through a means that is compact and highly efficient.